PROJECT SUMMARY/ABSTRACT To have an optimal response to the COVID-19 epidemic, it is important to understand the proportion of adults in the United States may have the virus that causes COVID-19, and how many have had it in the past and may have immunity. Currently available data are limited because the impact of asymptomatic and mildly symptomatic cases is unclear and many people are unable to access a test due to rationing, or may be otherwise unwilling to go for testing or care. This study will address this problem by conducting a national probability sample, where each address may be selected by chance, to develop estimates of the proportion of adults in the United States that are infected with the virus that causes COVID-19, and the proportion that has had the disease in the past and may now have immunity. We will use home-based testing techniques to facilitate participation in this national study. We will also use surveys to better understand participants in our sample. With these estimates, we will conduct disease modeling to understand different scenarios of the epidemic. We will also develop a website to provide information and data to the public.